"Being under attack"-->those three words help explain a lot. But maybe that attack is more psychological than real.
But I like your graphic. My time in a Canadian political party was that 90% of the party members really didn't do much for the party.
If they all had donated $50 to constiuency coffers, our election campaigns would have been much better funded. When we put on a fund raisier, we got 5% of our memembship out to the event--despite a mail and phone invitation. At our fund raisers, there were more party hacks from other consituencies than from local members.
I hear Trump rallies draw people from far away who enjoy the spectacle. Not really that much local participation.
Canadian author Paul St. Pierre had an interesting story about setting up a political rally. You have to make sure the venue is the right size. If it is not full, the media will lambast you. If it is too crowded and people can't get in, the media will lambast you--and some people will be annoyed because they came from far away to attend. A venue that is full and accomodates all people who want to be there gets the best results.